Re: [Discuss-gnuradio] ADC questions

[Brian Padalino]

On Wed, Sep 24, 2008 at 5:51 PM, Sebastiaan Heunis <address@hidden> wrote:
> Brian
>
> Sorry to bother.  I have one more question for now.  I wrote a Python
> app to generate an input signal, convert it to 12-bit two's complement
> and then bitshift it left by 3 and sign-extend it to get it to the
> representation used inside the FPGA.  My question now is that if I
> feed this input signal into the cordic, I'll somehow get it back to
> decimal in order to plot it in Matlab and see what happened.  Do I do
> the inverse that I previously did (shift it right by 3 and remove the
> sign extension and then take it from two's complement to decimal?)
> Let's say I take the signal from the cordic and pass it to the CIC
> filter.  When I want to have a look at the output of the CIC filter,
> can I also do the above to get the output to 12-bit decimal?

All you need to do is divide by the normalization factor of what 1.0
really is in a fixed-point representation.

>From the ADC, you will get a +/-2047 signal.  To get this to decimal
format, you need to divide by 2047.  Since you're shifting over to the
left by 3, you need to divide now by 16383 to get your +/- 1.0 decimal
values.

Does that make sense?

Brian